Axial air-gap type rotary electric machines include magnetic field elements and armatures, and they are desirable in terms of their reduced thickness and in terms of improved torque density with increased pole-face areas.
Although thrust forces are generated in the axial air-gap rotary electric machines, installing two magnetic field elements on mutually opposite sides of one armature or installing two armatures on mutually opposite sides of one magnetic field element, for example, will cancel out such thrust forces generated in the rotary electric machines.
In particular, installing two armatures per magnetic field element is desirable, This is because only one magnetic field element, which is usually adopted as a rotator, can reduce windage losses.
Patent documents 1 and 2 disclose rotary electric machines that include two armatures per magnetic field element. A magnetic field element disclosed in patent document 1 includes a plurality of magnets each having two pole faces having different polarities from each other, one of the pole faces facing one armature and the other of the pole faces facing the other armature. A magnetic field element disclosed in patent document 2 includes magnets on its end faces, one of the end faces facing one armature and the other of the end faces facing the other armature. In addition, patent document 3 discloses a technique relevant to the present invention.
Patent document 1: Japanese Patent Application Laid-open No. 2001-136721
Patent document 2: Japanese Patent Application Laid-open No. 2005-295757
Patent document 3: Japanese Patent Application Laid-open No. 2005-143276